October 2010 500mb pattern vs October 2017 is just about as opposite as you can get... LOL. Love it. I hope future generations will appreciate (either as comedy or sympathetically) the struggle we go through today trying to figure this out

You're not kidding.

I looked at every Nina year (even -ENSO, -0.2 or better) October & found nothing close. You will not find a matching October since 1979 for sure. I haven't looked before then because of climo, but wouldn't hurt. Now if you expand it to maybe mid-Sept to mid-Nov you might but I haven't looked

Right. The placement is similar to what we saw last year. But here, I was responding to Grace who found a bunch of east-based Ninas of varying intensity. I was saying I'd like to look at the OLR of those years, and in a case such as that where you have a bunch of ENSO events of the same base but varying intensity, the position of the greatest OLR anomalies (which should be similar amongst them all if they all behaved as expected (e.g., east-based Nina -> east-based forcing)) is more important than the magnitude of OLR anomalies (which depend upon the strength of the Nina, which was not a part of the selection of ENSO events).

In other words, I still stand by my post regarding the forcing this year behaving like last year so far. The magnitude of the OLR does appear to be a bit weaker but the greatest anomalies are located around the same latitude.

Side point:What's interesting is, although OLR has been weaker this year, MEI is stronger than last year. The value for AUG-SEP 2017 was -0.449, compared to -0.091 AUG-SEP 2016. Additionally, JUL-AUG 2017 to AUG-SEP 2017 featured a bigger drop (0.027 to -0.449) than JUL-AUG 2016 to AUG-SEP 2016 (0.186 to -0.091).

It's kind of an unfair comparison because this Nina is so much different from last year. Not only regarding the location of the Nina, but also the fact that we were almost 2 weeks past peak at this time last year. It looks like this Nina still has a solid 15-30+ days left until the Nina starts dying out.

NOAA has MEI ranks. Their definition:

QUOTE

How can one interpret these ranks? Given that there are 67-68 numbers in each column, the lowestnumber (1) would denote the strongest La Nina case for that bimonthly season, while the highestnumber (67 or 68) would indicate the strongest El Nino case. For instance, in December-January (DECJAN), the strongest La Nina was recorded in 1974, while the strongest El Nino occurred in 1983.

If we use percentiles (say, the lower and upper 30%iles) to define La Nina and El Nino, respectively, MEI ranks from 1-21denote strong to weak La Nina conditions, while 47-67 (48-68) denote weak to strong El Nino conditions. If one uses the quintile definition for (moderate or stronger) ENSO events, MEI ranks from 1-14would denote La Nina, while 54-67 (55-68) would denote El Nino. Finally, the comparison figures on thiswebsite refer to strong ENSO events, such as might be defined by the top 7 (upper decile)ranks, such as 1-7 for La Nina, and 61-67 (62-68) for El Nino.

In other words, focusing on Nina... you have a La Nina according to MEI if the rank is between 1-21. You have a moderate Nina if it's between 7-14. You have a strong Nina between 1-7.

September/October 2017 rank is 19.August/September 2017 rank was 21.September/October 2016 rank was 24. This was the lowest it got during the entire event.

It's been a while since I brought up the 1999-2000 analog on here, but I'm sticking to my guns (i.e. similarities 2 years after a major El Nino event, particularly given ongoing moderate La Nina forcing) until I see a reason not to. A while back I mentioned what I though to be a ~1 month delay in the 2017 vs 1999 observed patterns and I'm going to continue with that rationale.

Yup, there are differences but I am arguing that the similarities are more noteworthy. For example, the banana ridge extending from Japan to the Pac NW / Gulf of Alaska. Additionally, note the weak troughing over the central US and potent ridging across the Northeast/Southeast Canada. If this were a good analog then October 1999 should give a good clue of November 2017:

Looks like general troughing over the Gulf of Alaska, ridging over the 4-corners/southern plains, and troughing over SE Canada are a reasonable match. Clearly there are differences in magnitude of ridging near the Bering Sea/North Atlantic as well as the precise locations of trough/ridge axes, but I'm curious how it will look by the end of the month.

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For the first time in this event, all regions are below -1.0 anomaly on Tropicaltidbits page. Region 3 actually falls 0.23 short, but close enough.

Apparently quite a big spread westward. Here's what it all looks like

Also notice regions 1, 2, & 3 appear to have warmed quite a bit over last 7-10 days. Doesn't appear to be as much of a shift West, but rather a weakening of the Nina. Maybe temporary but that's what's happening. And of course since the waters are propagating from east to west, obviously the cooler waters out of those three regions are just now pushing into regions. 3.4 & 4.

Also notice regions 1, 2, & 3 appear to have warmed quite a bit over last 7-10 days. Doesn't appear to be as much of a shift West, but rather a weakening of the Nina. Maybe temporary but that's what's happening. And of course since the waters are propagating from east to west, obviously the cooler waters out of those three regions are just now pushing into regions. 3.4 & 4.

How is this evidence of a weakening Nina when region 1+2 is the only region that has meaningfully warmed per Tropicaltidbits? And maybe it's not a shift west, but it's absolutely a spread west.

Furthermore, there's a difference between the SSTA graphs that Tropicaltidbits offers and the official CPC numbers. That's why I specified that in my original post because I see that as just a preliminary first-guess of where the official weekly numbers will go.

In my humble opinion, we are seeing a bit of an "acceleration" of this Niņa evolution. I'll explain.

I've been waiting to see if that MJO wave in October was sufficient to initiate Kelvin wave activity. After looking at the observations, I believe that at least some EKW activity has begun, but the magnitude isn't great.

First is Tao data, this shows the sub surface warm tongue pushing east.ezgif_4_0848c76b21.gif ( 113.12K )
Number of downloads: 0

Similar to a digging trof, or a boat pushing through water, the "downwelling" action creates an "upwelling" just out in front. So I believe the downwelling west of the dateline is aiding in the upwelling to the east of it.

So, any weakening in the trades (even very weak enhanced trades) in the area I boxed out, will encourage this Kelvin wave activity. Remember, there's always a slope to the equatorial Pacific, and it's currently double the normal in this region.

How is this evidence of a weakening Nina when region 1+2 is the only region that has meaningfully warmed per Tropicaltidbits? And maybe it's not a shift west, but it's absolutely a spread west.

Furthermore, there's a difference between the SSTA graphs that Tropicaltidbits offers and the official CPC numbers. That's why I specified that in my original post because I see that as just a preliminary first-guess of where the official weekly numbers will go.

In my humble opinion, we are seeing a bit of an "acceleration" of this Niņa evolution. I'll explain.

I've been waiting to see if that MJO wave in October was sufficient to initiate Kelvin wave activity. After looking at the observations, I believe that at least some EKW activity has begun, but the magnitude isn't great.

First is Tao data, this shows the sub surface warm tongue pushing east.ezgif_4_0848c76b21.gif ( 113.12K )
Number of downloads: 0

Similar to a digging trof, or a boat pushing through water, the "downwelling" action creates an "upwelling" just out in front. So I believe the downwelling west of the dateline is aiding in the upwelling to the east of it.

Yea been thinking this for a bit now it seems as though the last MJO initiated something but failed to really couple up with it. I tend to agree we may see one of two things happen, one we could see another MJO spark up and help move this wave eastward with time and kind of stall the strengthening and maybe even weaken the nina state a little bit. Two we could see it sharpen real quick drop in a more localized area instead of spread over the basin and then begin to dwindle around maybe mid december either way it seems we are at about the peak of this event unless something throws a surprise out there.

...idee knows that some do not 'get' this 3-D view of the tropical Pacific Ocean...but very informative...frame060.png ( 34.79K )
Number of downloads: 0

...this shows SST's and temperatures to and below the thermocline...it also shows how much water builds up in the west Pacific courtesy of the strong convection center near Indonesia...and the prevailing trade winds...

...MJ (above) has valid points about the Nina perhaps peaking or past-peak and ... idee's gut feels a OKW...

...also notice the colder edge of the water is facing south...towards the end of their(south Hemisphere) Boreal Spring...the upwelling along the S.America coast should wane as their weather slows down into their Spring into Summer...a sloshback is well overdue...yet who knows...

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"Science cannot solve the ultimate mystery of nature. And that is because, in the last analysis, we ourselves are part of nature and therefore part of the mystery that we are trying to solve." - Max Planck

I don't follow. How do you know that the implications are on the cold side more than the warm side? I don't know how anyone can know the implications of this change when we don't know how forcing is going to shift, if it does... and if the HLB maintains.

I don't follow. How do you know that the implications are on the cold side more than the warm side? I don't know how anyone can know the implications of this change when we don't know how forcing is going to shift, if it does... and if the HLB maintains.

I didn't say it would be cold implications...but had the feel that warmth was your implication. Maybe I'm wrong...but I threw post in.

As I suspected... the eastern Pacific cooling was fake news. West Pacific warming wasn't fake news, though. But I wouldn't get comfortable with that because it appears a spread west and general intensifying of the Nina should be expected in the next 2 weeks, maybe more.